The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.
Most common built-in tests for High Speed Input/Output (HSIO) employ two identical Pseudo-Random Binary Sequence (PRBS) generators, one located in a transmitter (TX) and the other in a receiver (RX). Both PRBS must be synchronized, allowing the RX to replicate exactly what the TX generates. The RX compares received data transmissions with what was expected and if differences between received data transmissions and the transmissions that were generated in the test data set identifies failures. The test patterns generated or checked by PRBS are limited by the employed LFSR polynomial. The LFSR used in PRBS can usually supply a single sequence of pseudo-random patterns. If additional patterns were required, they can be implemented by adding extra hardware.
Many High-Speed Input/Output (HSIO) systems also encode data for transmission, for example using a 10-bit DC-balanced clock-embedded encoding scheme. The IBM 8B/10B encoding scheme is an example of such a scheme and encodes 8-bit values into 10-bit codewords. Each 8-bit value has two assigned codewords allowing the number of 1's and 0's in a data stream to be balanced. When the number of 1's and 0's are the same or substantially the same over some specified number of codewords the signal levels DC-voltage level balanced over that specified number of codewords. The difference between the number of 1's and 0's can be defined as disparity or DC value. DC-balancing is to reduce inter-symbol interference (ISI) problem and to make the AC coupling more applicable. If, for example, number of 1's or 0's in the sequence of codeword is biased to 1 (or 0), it is difficult to transmit a 0 (or 1) symbol because it requires a lot more energy to overcome the biased state of the channel. The transmitted opposite state symbol may therefore be recovered in error. If, say, three consecutive codewords (0000000000, 0000000010, 0000000000) were transmitted over the channel, the symbol may be lost due to ISI problem. Many High-Speed I/O (HSIO) systems uses AC coupling that uses a capacitor between the transmitter and the receiver to block a low frequency voltage noise coming from power supply and ground. Low frequency data streams, such as for example shown above, may be blocked and may result in the receiving signal voltage distortion and error. To keep the receiving data error within the specified target, the maximum allowed disparity of a codeword is specified at the transmission. The maximum disparity allowed in the transmission codewords is defined as DC-balance. The IBM 8B/10B coding scheme is know in the art and described in the paper by A. X. Widmer and P. A. Franaszek, entitled “A DC-Balance, Partitioned-Block, 8B/10B Transmission Code”, IBM J. Res. Develop., Vol. 27, No. 5, PP. 440-451, September 1983; which paper is hereby incorporated by reference.
One disadvantage of conventional PRBS generators, systems and methods is that they often lack features for testing silicon chips, such as online and/or offline testing and/or debugging of the chip. Online and offline debugging or testing refers to tests run during field use and testing respectively. Normal mode refers to using a chip under normal usage circumstances, while test mode refers to using a chip in a test environment. Having both online and off-line may be advantageous because the quality of a communication channel can be tested and determined in the field.
An additional disadvantage of conventional PRBS systems and methods is the requirement that the TX PRBS and RX PRBS must be synchronized so that a proper comparison of know transmitted test data may be compared to the received data and any errors or failures identified. When using a TX PRBS and RX PRBS system, if a transmission error occurs causing synchronization failure during a test, the system cannot recover. The test results after such a synchronization failure may not be meaningful.
There therefore remains a need for systems and methods that overcome the problems and limitations of conventional PRBS.